1. Technical Field
The present invention relates to fluid-dynamic-pressure bearing manufacturing methods, to spindle motor manufacturing methods, and to spindle motors and recording-disk drives.
2. Description of the Related Art
In recent years, the amount of information that is recorded per unit area on discoid recording media in hard-disk and like recording-disk drives has been increasing, and the information density has been on the rise. The increasing recording density has led to calls for stably supporting the discoid recording media under high-speed rotation.
Recording-disk drives, meanwhile, are finding applications other than in stationary computers, such as desk-top and server machines, in which the drives have been traditionally employed, and are being used in vehicular devices, portable devices, and other mobile devices. Such mobile applications have led to rising demands for impact resistance and longevity-demands without precedent in implementations in which the drives are employed under environments, as has conventionally been the case, that do not subject the drives to vibration and shock.
Against this backdrop, the development of bearings for stably supporting disk-drive rotor units under high-speed rotation has been ongoing.
In order that the bearings meet this demand, considerations of paramount importance are:
(A) Improvement in the sealing performance of the bearing's capillary seal section;
(B) Improvement in the ability to prevent wetting diffusion along the surfaces in the vicinity of the capillary seal; and
(C) Improvement in the joint strength of the components that constitute the dynamic-pressure bearing and the spindle motor.
Consideration (A)
Fluid-dynamic-pressure bearings are composed of a journal unit and a journal-support unit, between which is formed a narrowed micro-gap. A lubricating fluid such as oil is retained within the gap. An oil sealing mechanism referred to as a capillary seal section is provided in the part of the bearing in which the micro-gap is open to the external atmosphere. The capillary seal section is of a form in which the gap between the journal and, opposing the journal, seal surfaces on the bearing's journal-support side gradually flares going axially upward. A boundary surface between the oil and the external atmosphere forms in the capillary seal section.
If the lubricating fluid is not sealed in by the capillary seal section, the fluid ends up leaking out to the exterior. As a consequence, the lubricating fluid retained in the micro-gap runs short, ultimately curtailing the lifespan of the bearing. In bearing implementations in miniature spindle motors in particular, since the gross amount of oil retained inside the bearing is very little, if even a slight amount of the lubricating fluid manages to leak out, an oil shortfall is liable to occur. Furthermore, the problem of weak sealing performance in capillary seals can allow shock or other impact on the bearing to disturb the integrity of the seal boundary surface.
Keeping the angle of contact between the oil and the components that constitute the capillary seal section small is crucial to enhancing the strength of capillary seals.
Consideration (B)
Oil repellant is applied to the surfaces of the components that constitute the outer side of the capillary seal section. Applying oil repellant prevents lubricating fluid from the capillary seal section from migrating along the bearing component surfaces to the bearing exterior by wetting-diffusion.
The way oil repellants are applied is to spread repellant that has been dissolved in a solvent onto the component surfaces, and vaporize the solvent to get the oil repellant to adhere to the surfaces.
Nevertheless, the wettability of the oil repellant for the seal component surfaces is poor, which has meant that the repellant-to-surface adhesiveness has not been satisfactory. Consequently, oil mop-up or associated concluding operations in manufacturing dynamic-pressure bearings cause the oil repellant to peel off easily. Although processes such as striating the components or spreading the oil repellant on thickly have been implemented to date on account of the behavior of the repellant, such processes elevate the component cost, and, moreover, have not amounted to a fundamental solution.
Consideration (C)
Spindle motors for hard-disk drives are furnished with a base component and, anchored to the base component, a cylindrical sleeve housing that serves as a stator-side bearing component. The outer circumferential surface of the sleeve housing is, by an interposed adhesive, fixed to the inner circumferential surface of a mounting hole formed in the base component.
The slightest warpage or deformation in spindle-motor bearing components becomes a problem particularly in fluid-dynamic-pressure bearings, in that the bearing gaps are extraordinarily narrow. On that account, in the plurality of inter-component junctions, adhesive anchoring by means of an adhesive agent is often employed instead of welding, in which thermal deformation is liable to occur.
Especially under environments, such as in mobile and vehicular devices, that place vibration and shock on the bearings, particularly large loads are placed on the joints between components. More particularly, the ability to withstand serious shock—in excess of 1000 Gs—can be mandatory in situations in which there is a likelihood of the devices being dropped. Consequent on the scaling down of spindle motors, however, is an abridgement of the inter-component binding length, which has made improving the binding strength a challenge.